The young Auckland Hearts bowler delivered four dot balls to Sparks batter Eden Carson to start the final over, which the Sparks needed 10 runs from to win.
When Carson got bat to ball, it landed in the hands of Hearts captain Maddy Green.
Illing produced another dot to finish the over and secure a nine-run win for the Hearts at Eden Park tonight.
Chasing 147 to win the game, Caitlin Blakely did her best to get her side across the line with an unbeaten 50 on a bouncy wicket.
But the Sparks lost too many wickets through the middle, leaving a tough ask for their middle order.
Sparks captain Suzie Bates praised Blakely’s efforts and what she felt was one of the Sparks' better chases this season.
"I think we did extremely well to take it to the last over," Bates told TVNZ after the game.
"I thought Caitlin Blakely and Hayley Jensen’s partnership really kept us in the game, so outstanding innings from Caitlin.
"Ten off six in the last over, you’re in the game so a lot of learnings from that last over to take forward in the tournament."
The Sparks started strong with the ball and had the Hearts under pressure in the opening over when Linsey Smith caught Emma Black’s final delivery.
It sent White Fern Izzy Gaze out for a duck, and fellow opener Saachi Shahri went in the next over.
She clipped her shot down to Black at fine leg, leaving the Hearts eight for two.
But Green anchored her side’s innings, as she has done all season with an unbeaten knock of 75 off 56 balls.
Green had help from Prue Catton this time, who had one of her best innings of the season.
They combined for a 109-run partnership and dug the Hearts out of an early scare.
It felt as though the Sparks had no answers for the pair who ticked over the scoreboard pressure, and pushed for twos.
But Molly Loe finally made the breakthrough when Catton (39) chopped on her delivery in the 16th over.
Anna Browning went for eight and then Bella Armstrong was run out for a duck after some fantastic work from Carson.
Josie Penfold was then run out by wicket keeper Polly Inglis for a duck, and the Hearts finished 146 for six.
Sparks opener Bella James went for a duck, but Felicity Robertson came to the crease aggressive with Bates.
They were proactive in trying to eat into the run chase early, as Molly Penfold struggled to find their lines.
Once Penfold got her line right, she bowled Robertson (18), who had punished Penfold for another four the ball earlier.
Trying to attack the ball, Inglis went hard, but smacked her shot straight up in the air landing in the hands of Josie Penfold.
Fran Jonas took the big wicket of Bates in the eighth over and Gain went for an lbw the same over, putting pressure on the Sparks at 58 for five.
Blakely and Jensen provided hope with a 47-run partnership, but that was cut short when Jensen was unlucky, chopping a delivery off her back leg and leaving for 24.
Smith (11) went in the 19th over and Illing did the rest.
Auckland Hearts
S Shahri c Black b Jensen 7 (7)
I Gaze c Smith b Black 0 (5)
M Green not out 77 (56)
P Catton b Loe 39 (40)
A Browning c Bates b Carson 8 (7)
B Armstrong run out Carson 0 (1)
J Penfold run out Smith/Inglis 1 (3)
M Penfold not out 1 (1)
Extras (4b, 9w) 13
Total (for 6 wkts, 20 overs) 146
Fall: 1-1, 2-8, 3-111, 4-130, 5-130, 6-133
Bowling: E Black 4-0-22-1, H Jensen 3-1-16-1, L Smith 4-0-39-0, E Carson 4-0-25-1, S Bates 2-0-18-0, M Loe 3-0-22-1
Otago Sparks
S Bates b Jonas 18 (20)
B James c Gaze b Illing 0 (1)
F Robertson b M Penfold 18 (9)
P Inglis c J Penfold b Jonas 1 (6)
C Blakely not out 50 (40)
O Gain lbw Jonas 1 (3)
H Jensen b Browning 24 (25)
L Smith c Catton b Hucker 11 (9)
E Carson c Green b Illing 1 (6)
E Black not out 0 (1)
Extras (8b, 1lb, 4w) 13
Total (for 8 wkts, 20 overs) 137
Fall: 1-3, 2-31, 3-32, 4-56, 5-58, 6-105, 7-132, 8-137
Bowling: B Illing 4-1-23-2, M Penfold 4-0-25-1, F Jonas 4-0-23-3-, J Penfold 1-0-8-0, A Hucker 4-0-29-1, A Browning 3-0-20-1
Result: Auckland won by nine runs
